Why are you doing medicals now? It has zero benefit and potentially causes problems. For example, we have a member who did this and just received grant. 11 months after medicals. As a result they have a month to make a very expensive trip to Australia or face potential visa cancellation.

I can only comment on the issue about how they cope with the move as we don't have children, so can't comment on the aspects associated with that.
We moved the other way, Oz to UK with our little chihuahua. He is a very nervous little thing who has never spent more than 30 minutes away from his mum. He also has a number of medical issues. So, we were obviously very worried. He arrived fine, just hungry and a bit jet lagged. It was a big difference in things as we moved from Perth to central Scotland, to a place notorious for cold weather and snow and he never got on with even the Perth winter. But he is loving life and having as much fun as ever - he was running around in the park yesterday even though it was 0c.

If you look through forum posts, you will find a fair number lodge in 2013 just getting grant now.
Visa processing times are blowing out and becoming very unpredictable. To give some context, when I applied for my first visa, processing took 3 days, today it is about 6 months. My PR visa took 5 days, today, it isn't uncommon to take 18 months. The remaining relative visa was about 8 years. Today, it is 56 years.

If you have just lodged, then the visa isn't coming in the next couple of months. The department are currently processing applications lodged about five years ago. However, processing times have recently blown out and you should allow about eight years.

It does not guarantee a PR visa. It means you may be eligible for the work ready programme, which would allow you to pass a skills assessment. However, all other or criteria would apply such as points and most importantly that the occupation is still eligible. This is important as the lists change at least once a year. Last year alone over 200 occupations were removed.

The issue is that if your business effectively changed - new place of work, new abn, new conditions before the grant, you and the business should have notified the department and because you didn't, could lead to your visa being cancelled. I recommend professional advice

Be very careful on two aspects. First, never ever take advice from immigration. I know that sounds odd, but you would be amazed how often they give bad advice and they have a legal indemnity for the problems that causes - the official requirement is that if need advice, you should speak to a registered migration agent.
Second, the policy as far as I am aware has not changed from what Nemesis has said. Which is that if you fail to make first entry by the first entry date, visas are cancelled

If the changes were prior to the visa being granted, then I would say you have a good chance. If they were prior, forget it, as the transfer of your job to what is effectively a different business should have been reported to the department and the failure to do so could still cause issues.

Being in China makes no difference.
You can combine income and savings
Income from rental property is not regarded as savings, but as income.
if you go down the income route, you need to prove an income of £18600 in the last twelve months and have job paying £18600.
If you go down the savings route, you need to have the cash in the bank for at least 12 months unless it is from the sale of your main residence.
Your wife can visit on a tourist visa, but must be off shore for visa grant

Yes, you can apply for a 489 or a 189 or a 190 if you meet the eligibility criteria.
The benefits are if you want to remain in Australia? At the moment, you will be returning to your home country at the end of the 457. A 489, is a provisional visa, which if you meet the requirements of living in a regional area for two years and working in a regional area for one year, becomes permanent. It isn't tied to a employer and you can work for anyone doing any occupation